The present invention relates to a process for the production of multi-thickness and/or multi-material blanks of metal sheet, known as xe2x80x9cTailored Welded Blanksxe2x80x9d (TWBs).
TWBs are used in numerous technical sectors whenever it is necessary to produce metal pieces having differentiated strengths. A typical field of use is the sector of construction of vehicle bodies. A TWB generally consists of two or more pieces of metal sheet having different thicknesses or being made of different materials that are welded together. In the simplest case, the line of jointing between the blanks is rectilinear, but in many cases it is necessary to make TWBs with non-linear jointing lines, or else with jointing lines including a number of rectilinear stretches having different angles.
Traditional plants for the production of TWBs on an industrial scale envisage the use, as starting material, of pieces of metal sheet cut using shearing machines. However, in current practice, unless high-precision shearing machines are used, and hence ones having a very high cost, the edges of said pieces of metal sheet have a rough surface finish, or in any case a surface finish such as not to enable convenient butt welding of the edges themselves. The rough pieces of metal sheet then undergo a preliminary blanking operation, by means of which pieces are obtained that have precise dimensions and a good degree of surface finish along the welding edges. At the end of the blanking operation, the pieces are positioned in a welding system where butt welding of two or more pieces having different thicknesses is performed along a welding path coinciding with the line of jointing between the pieces. The welding operation can be performed using laser-welding machines.
The conventional technology for the production of multi-thickness and/or multi-material blanks described above presents various drawbacks. A first drawback is represented by the fact that, at the end of the blanking operation, an operation is required for relative positioning of the pieces to be welded and for referencing of the pieces to the co-ordinate system of the welding plant. Usually, the said referencing operation is carried out using mechanical locator blocks, but this system may give rise to numerous problems and difficulties in the case of pieces with complex shapes that are to be welded together along non-rectilinear paths. A second drawback is represented by the need to use high-precision shearing machines that are very costly in terms of investment and maintenance, or else to perform a preliminary blanking of the pieces to be welded. The said blanking operation produces a considerable amount of waste material and requires costly and rigid equipment which needs to undergo routine maintenance and must be replaced in the case where the shape and/or size of the pieces to be blanked varies.
The purpose of the present invention is to provide a process for the production of multi-thickness and/or multi-material blanks that enables the aforesaid drawbacks to be overcome.
According to the present invention, the above purpose is achieved by a process having the characteristics that form the subject of claim 1.